The most popular tumor management approach is through surgical means. Surgical treatment of cellular tissues usually exposes both the target and intervening tissues to substantial trauma and causes a great deal of damage to healthy tissues. During a surgical procedure, precise placement of a treatment device is difficult because of the location of a target tissue in the body or the proximity of the target tissue to obstructions or easily damaged critical body organs, such as nerves or blood vessels. New products with an emphasis on minimally invasive approaches are being progressively developed to replace the traumatic nature of traditional surgical procedures.
There has been a relatively significant amount of activity in the area of high energy as a tool for treatment of tumors. It is known that elevating the temperature of tumors is helpful in the treatment and management of cancerous tissues. The mechanisms of selective cancer cell eradication by high-energy doses are not completely understood. However, Edwards et al. in U. S. Pat. No. 5,536,267 hypothesized certain cellular effects of high energy on cancerous tissues. Nevertheless, treatment methods for applying heat to tumors include the use of direct contact radiofrequency (RF) applicators, microwave radiation, inductively coupled RF fields, ultrasound, and a variety of other simple thermal conduction techniques.
In an illustrative example, high frequency currents are used in electrocautery procedures for cutting human tissues, especially when a bloodless incision is desired or when the operating site is not accessible with a normal scalpel but presents an access for a thin instrument through natural body openings such as the esophagus, intestines, uterus, or urethra. Examples include the removal of prostatic adenomas, bladder tumors or intestinal polyps. In such cases, the high frequency current is fed by a surgical probe into the tissue to be cut. The resulting dissipated heat is controlled so that no boiling and vaporization of the cell fluid occurs at this point. The frequency of the current for this use must be above ca. 300 kHz in order to avoid any adverse effect such as nerve and/or muscle responses.
Destruction of cellular tissues in situ has been used in the treatment of many diseases and medical conditions alone or as an adjunct to surgical removal procedures. It is often less traumatic than surgical procedures and may be the only alternative where other procedures are unsafe. Ablative treatment devices have the advantage of using a destructive energy that is rapidly dissipated and reduced to a non-destructive level by conduction and convection forces of natural body process. Ablative energy may also be controlled by a closed-loop temperature control mechanism.
The same is true for ablation of the tumor itself through the use of RF energy. Different methods have been utilized for the RF ablation of masses such as tumors. Instead of heating the tumors it is ablated through the application of RF energy. This process has been difficult to achieve due to a variety of factors, such as access site, probe location, electrode positioning, energy level, et al. Among them, the most critical factor is the positioning of the RF ablation electrode to effectively ablate all of the mass by controlled delivery and monitoring of RF energy to achieve successful ablation without damage to non-tumor tissue.
There have been a number of different treatment methods and devices for minimally invasively treating tumors. One such example is an endoscope that produces RF hyperthermia in tumors, as described in U.S. Pat. No. 4,920,978. In U.S. Pat. No. 4,920,978, an endoscope for RF hyperthermia is disclosed. In U.S. Pat. No. 4,565,200, an electrode system is described in which a single entrance tract cannula is used to introduce an electrode into a selected body site. In U.S. Pat. No. 5,458,597, a RF probe with fluid infusion capability is described. Similarly, in U.S. Pat. No. 5,536,267, a multiple electrode ablation apparatus with fluid infusion means is described. For the system with a closed-loop temperature control mechanism, the fluid infusion means for the sole purpose of cooling off the tissues may not be required. Recent clinical studies have indicated that the delivered RF energy is rapidly dissipated and reduced to a non-destructive level by conduction and convection forces of natural body process. In all examples, the tissue destruction energy and/or substances have been used to destroy malignant, benign and other types of cells and tissues from a variety of anatomic sites and organs. Tissues treated include isolated carcinoma masses and target tissues in organs such as prostate, glandular and stromal nodules characteristic of benign prostate hyperplasia.
There is a need for a RF ablation apparatus that is useful for treatment and reduction of undesired body tissues by minimally invasive procedures. It would be desirable for such a device to surround the tumor with treatment electrodes in an essentially circular fashion, and to define a controlled ablation amount of RF energy by monitoring the temperature and controlling the energy delivered.